1. Go to the 1/1 of any month
2. Your "mom" should give you a letter to celebrate the new year
3. She'll give you a present of 10 000 bells
4. Go exactly one year to the future and you'll receive another letter
5. Repeat this process
NOTE: This process takes a while. And you WILL get weeds with it.
Also if a neighbour has a birthday in January they'll keep sending you letters unt il they actually move which can take ten years!